WO1998049244A1

WO1998049244A1 - Aqueous coating agent

Info

Publication number: WO1998049244A1
Application number: PCT/EP1998/002548
Authority: WO
Inventors: Rainer BÜRSTINGHAUS; Maximilian Bendix; Heinz-Peter Rink
Original assignee: Basf Coatings Ag
Priority date: 1997-04-30
Filing date: 1998-04-30
Publication date: 1998-11-05
Also published as: EP0977817A1

Abstract

An aqueous coating agent contains (a) at least one binder, (b) water, (c) optional catalysts, auxiliary substances, degassing agents, levelling agents, U.V.-absorbers, radical catchers, non-ionic thickeners, biocides, water-retaining agents and/or anti-oxidants, (d) optional colouring and/or effect-producing pigments, (e) optional cross-linking agents. This coating agent is characterised in that it can be prepared by the following steps: (A) the binder is prepared in an organic solvent; (B) the thus obtained binder solution is dissolved or dispersed in critical or supercritical carbon dioxide in critical or supercritical carbon dioxide pressure and temperature conditions; (C) at least 80 % of the organic binder, relative to the total content of organic binders, is extracted from the thus obtained solution or dispersion and optionally recovered; (D) the thus obtained, solvent-impoverished solution or dispersion is added to water in subcritical carbon dioxide pressure and temperature conditions.

Description

Aqueous coating agent

description

The invention relates to an aqueous coating agent with (a) at least one binder, (b) water, (c) optionally, catalysts, auxiliaries, degassing agents, leveling agents, UV absorbers, radical scavengers, nonionic thickeners, biocides, water retention agents, organic solvents and / or antioxidants, (d) optional, color and / or effect pigments, (e) optional, crosslinking agents, a process for producing such a coating agent and use of such a coating agent. A coating composition according to the invention can be a primer composition, a fuller composition, a decorative, ie color and / or effect-forming topcoat composition or a clearcoat composition. In the case of a filler, customary fillers are also used. Such coating agents are required in a variety of areas, but in particular in the area of automotive painting. The clear lacquer coating in particular forms a protective layer against damaging environmental influences for the substrate or the underlying lacquer layers. A clear varnish is practically free of pigments and the resulting coating is practically transparent in the visible area. By applying a clear coat over a color and / or effect-forming top coat, a coating which meets particularly high optical requirements is obtained. The substrate can be any molded part. In the case of automotive painting, the substrate is usually already coated in addition to the actual structural support such as primer, filler, color coating and / or effect coating. Then the clear coat is the top layer. In general, a film-forming substance is referred to as a binder. A binder can consist of various components, for example one or more base binders and optionally one or more crosslinking agents for the base binders. The base binder can also be self-crosslinking and consequently form the only binder component. Of course, it is possible to work with several different basic agents and / or several different crosslinking agents. The ready-to-apply, in particular viscosity-adjusted, coating is referred to as the coating agent. Coating agents according to the invention can in particular be formed as powder coating slurries by suitable choice of the binders and, if appropriate, crosslinking agents and, if appropriate, (wet) grinding to a desired particle size. In this case, the particles generally contain the base binder, possibly the crosslinking agent and, if appropriate, powder coating additives.

Various technologies are known for the production of aqueous coating compositions, which are more environmentally compatible in processing than "coating technically superior" coating compositions based on organic solvents. On the one hand, a binder can be produced in organic solution and then converted into an aqueous phase The polymerization of the binder is carried out directly in the aqueous phase In any case, it is necessary that the binder and possibly the crosslinking agent carry dissociable groups, for example carboxyl groups produced coating, especially the weather resistance, are adversely affected. For these reasons, so-called powder coating slurries have been developed, the special coating components suitable for powder coating formulations first being prepared in an organic solution, mixed with one another, then ground and dispersed in an aqueous phase during or after the grinding. However, special chemical-chemical boundary conditions must also be observed here if a coating that meets all the requirements is to be able to be produced.

Compared to the prior art, the invention is based on the technical problem of specifying an aqueous coating composition which, in terms of its coating properties, in particular the properties of the coating produced therefrom, corresponds to the coating compositions based on organic solvents.

To solve this technical problem, the invention teaches that the coating agent can be prepared by (A) producing the binder in an organic solvent, (B) the binder solution obtained in step (A) in critical or supercritical carbon dioxide at critical or supercritical pressure. and temperature conditions of the carbon dioxide are dissolved or dispersed, (C) at least 80% of the organic solvents, based on the total content of organic solvents, are withdrawn from the solution or dispersion obtained in step (B) and optionally recovered, (D) die Solvent-reduced solution or dispersion obtained in stage (C) is introduced into water under subcritical pressure and temperature conditions of the carbon dioxide. - The critical point of carbon dioxide is through that characterized the following thermodynamic data: critical pressure = 74 bar (üDr), critical temperature = 31 ° C, density = 468 kg / m ³ . Carbon dioxide is critical if states are set in the pV diagram on the 31 ° C isotherm running through the critical point, and supercritical if states above these isotherms are set. The term solvent-reduced refers to stage (B) from organic solvents carried along from stage (A).

With regard to the binders to be used, it is preferred if a customary powder clear coat binder is prepared in process step (A). Component (c) and / or (d) and / or (e) can either be introduced in step (A) and / or (B) and / or added in a step (E) following step (D) become. It is preferred if component (e) and at least part, based on the respective component per se or on the total amount of the respective component, component (c), with the exception of the thickeners, is introduced in stage (B).

Component (A) can be a binder containing epoxy groups. For example, component (A) can be obtainable by copolymerizing an ethylenically unsaturated monomer with at least one epoxy group per molecule and at least one ethylenically unsaturated monomer free of epoxide groups, at least one of the monomers being an ester of acrylic acid or methacrylic acid, and being an epoxy-free monomer can optionally be a vinyl aromatic compound, preferably styrene. A straight-chain, aliphatic dicarboxylic acid can be used as the crosslinking agent and / or a carboxy-functional polyester can be used. A preferred embodiment of the invention is characterized in that the coating agent is formulated as a clear lacquer, ie it is free from pigments or only contains transparent pigments.

In the production of the coating agent, stage (B) can be carried out by means of a jet nozzle reactor. Step (D) can be carried out by embedding the reduced-solution or dispersion in water obtained in step (C) under normal conditions or, on the other hand, elevated but subcritical pressure and temperature conditions.

The invention further teaches a process for the preparation of an aqueous coating composition according to one of Claims 1 to 8, which is characterized in that (A) the binder is prepared in an organic solvent, (B) the detergent solution obtained in step (A) is critical or supercritical carbon dioxide is dissolved or dispersed under critical or supercritical pressure and temperature conditions of the carbon dioxide, (C) at least 80% of the organic solvents, based on the total content of organic solvents, are withdrawn from the solution or dispersion obtained in step (B) and optionally be recovered, (D) the solvent-reduced solution or dispersion obtained in stage (C) is introduced into water at subcritical pressure and temperature conditions of the carbon dioxide, and a use of an aqueous coating composition according to one of Claims 1 to 8 for the production of a coating provided with a coating Substrate, preferably one painted car body or a car body part. All of the above and subsequent explanations attached to the coating agent itself apply analogously to the method according to the invention and the use according to the invention. If more information on components in textual contexts is explained below, this information, and each individually, can be combined with other information that is not made in the relevant textual context, provided that this makes technical sense. This applies in particular to quantitative parameters, which can be provided independently of each other.

The invention uses the critical or supercritical carbon dioxide as an intermediate solvent which, on the one hand, permits the removal of the organic solvents and, on the other hand, subsequently enables a "redissolution" or "redispersion" in water. The result is a coating agent which, in terms of binder chemistry, corresponds to that with organic solvents, but is reduced in solvent, preferably practically free of organic solvents. On the other hand, the effort associated with processing binders in critical or supercritical carbon dioxide is avoided since water is ultimately the solvent or dispersion medium. Conventional and possibly already existing application techniques can therefore be used.

It is understood that within the various variants of the invention it is possible to work with wetting agents which ensure adequate wetting of binder particles with organic solvents and / or critical or supercritical carbon dioxide and / or water. Furthermore, a wide variety of common can be used in general Paint additives are used, which are given below in concrete contexts as examples.

In the following the invention SITUATE designated binder, in particular clear coat binder are exemplified in an individual ^¬ for all variants. For the sake of simplicity, the binders are all referred to below as clear lacquer binders, although the coating agents obtained in this way can in principle also contain coloring and / or effect pigments.

On the one hand, powder coating formulations of the following basic structure can be used as clear coating binders. A powder coating comprising al) at least one epoxy-containing binder with a content of 30 to 45%, preferably 30 to 35% of glycidyl-containing monomers, optionally with a content of vinyl aromatic compounds, preferably styrene, a2) at least one crosslinking agent, preferably straight-chain, can be used , aliphatic dicarboxylic acids and / or carboxy-functional polyesters and a3) optionally catalysts, auxiliaries, additives typical for powder coatings, such as degassing agents, leveling agents, UV absorbers, radical scavengers, antioxidants.

Suitable epoxy functional binders for the powder coating are, for example, epoxy group-containing polyacrylate resins which can be prepared by copolymerizing at least one ethylenically unsaturated monomer which contains at least one epoxy group in the molecule with at least one further ethylenically unsaturated monomer which does not contain any epoxy group in the molecule. wherein at least one of the monomers is an ester of acrylic acid or methacrylic acid. Such epoxy group-containing polyacrylate resins are known, for example, from EP-A-299 420, DE-B-22 14 650, DE-B-27 49 576, US-A-4, 091, 048 and US-A-3, 781, 379) .

Examples of ethylenically unsaturated monomers which contain no epoxy group in the molecule are alkyl esters of acrylic and methacrylic acid which contain 1 to 20 carbon atoms in the alkyl radical, in particular methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate and Called 2-ethylhexyl methacrylate. Further examples of ethylenically unsaturated monomers which contain no epoxide groups in the molecule, acid amides, such as e.g. Acrylic acid and methacrylic acid amide, vinyl aromatic compounds such as styrene, methyl styrene and vinyl toluene, nitriles such as acrylonitrile and methacrylonitrile, vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride, vinyl esters such as e.g. Vinyl acetate and hydroxyl group-containing monomers such as e.g. Hydroxyethyl acrylate and hydroxyethyl methacrylate.

The epoxy group-containing polyacrylate resin usually has an epoxy equivalent weight of 400 to 2500, preferably 420 to 700, a number average molecular weight (determined by gel permeation chromatography using a polystyrene standard) from 2,000 to 20,000, preferably from 3,000 to 10,000, and a glass transition temperature (T _G ) from 30 to 80, preferably from 40 to 70, particularly preferably from 40 to 60 ° C (measured with the aid of differential scanning calorimetry (DSC)). 50 ° C. is very particularly preferred. Mixtures of two or more acrylic resins can also be used. The epoxy group-containing polyacrylate resin can be prepared by polymerization using generally well-known methods.

Suitable crosslinkers are carboxylic acids, in particular saturated, straight-chain, aliphatic dicarboxylic acids with 3 to 20 C-a-toe in the molecule. Decane-1, 12-dicarboxylic acid is very particularly preferably used. To modify the properties of the finished clearcoat slurries, other crosslinking agents containing carboxyl groups may also be used. Examples include saturated, branched or unsaturated straight-chain di- and polycarboxylic acids and polymers with carboxyl groups.

Powder coatings which contain an epoxy-functional crosslinker and an acid-functional binder are also suitable.

Suitable acid-functional binders are, for example, acidic polyacrylate resins which can be prepared by copolymerizing at least one ethylenically unsaturated monomer which contains at least one acid group in the molecule with at least one further ethylenically unsaturated monomer which does not contain any acid group in the molecule.

The epoxy group-containing binder or the epoxy group-containing crosslinking agent and the carboxyl or the binder are usually used in an amount such that 0.5 to 1.5, preferably 0.75 to 1.25, equivalents of carboxyl groups are present per equivalent of epoxy groups. The amount of carboxyl groups present can be determined by titration with an alcoholic KOH solution. The binder preferably contains vinyl aromatic compounds, especially styrene. However, in order to limit the risk of cracking, the content is not more than 35% by weight. 10 to 25% by weight are preferred.

The powder coating slurries or powder coating particles obtained may contain one or more suitable catalysts for epoxy resin curing. Suitable catalysts are phosphonium salts of organic or inorganic acids, quaternary ammonium compounds, amines, imidazole and imidazole derivatives. The catalysts are generally used in proportions of 0.001% by weight to about 2% by weight, based on the total weight of the epoxy resin and the crosslinking agent.

Examples of suitable phosphonium catalysts are ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium thiocyanate, ethyltriphenylphosphonium acetate-acetic acid complex, tetrabutylphosphonium iodide, tetrabutylphosphonium acid-phosphonium-bromonium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-phosphoronium-and-tetrabutyl-phosphonium-ammonium bromide. These and other suitable phosphonium catalysts are e.g. described in U.S. Patent 3,477,990 and U.S. Patent 3,341,580.

Suitable imidazole catalysts are, for example, 2-styrylimidazole, 1-benzyl-2-methylimidazole, 2-methylimidazole and 2-butylimidazole. These and other imidazole catalysts are described, for example, in Belgian Patent No. 756,693. In addition, the powder coating formulations may also contain auxiliaries and additives. Examples of these are leveling agents, antioxidants, UV absorbers, radical scavengers, trickling aids and degassing agents, such as, for example, benzoin. Leveling agents based on polyacrylates, polysiloxanes or fluorine compounds are suitable. Antioxidants that can be used are reducing agents such as hydrazides and phosphorus compounds and free radical scavengers, for example 2,6 di-tert-butylphenol derivatives. UV absorbers that can be used are preferably triazme and benzotriphenol. 2,2,6,6 tetramethylpiperidine derivatives are preferably used as radical scavengers.

It is recommended that the aqueous phase of stage (D) is an aqueous dispersion containing a) at least one nonionic thickener and b) optionally catalysts, auxiliaries, defoamers, dispersion auxiliaries, wetting agents, preferably carboxy-functional dispersants, antioxidants, UV absorbers, radical scavengers, small amounts of solvents, leveling agents, biocides and / or water retention agents.

When using a non-ionic thickener, it is preferred to use non-ionic associative thickeners. Structural features of such associative thickeners are: aa) a hydrophilic structure which ensures sufficient water solubility and ab) hydrophobic groups which are capable of associative interaction in the aqueous medium. For example, long-chain alkyl residues, such as dodecyl, hexadecyl or octadecyl residues, or alkaryl residues, such as octylphenyl or nonylphenyl residues, are used as hydrophobic groups. Polyacrylates, cellulose ethers or are particularly preferred as hydrophilic frameworks Polyurethanes used that contain the hydrophobic groups as polymer building blocks. Polyurethanes which contain polyether chains as building blocks, preferably made of polyethylene oxide, are very particularly preferred as the hydrophilic frameworks. In the synthesis of such polyether polyurethanes, the di- and / or polyisocyanates, preferably aliphatic diisocyanates, particularly preferably optionally substituted 1, 6-hexamethylene diisocyanate, are used to link the hydroxyl-grouped polyether units with one another and to link the polyether units with the hydrophobic end group units which can be, for example, monofunctional alcohols and / or amines with the long-chain alkyl radicals or aralkyl radicals already mentioned.

Furthermore, the aqueous phase can contain catalysts, leveling agents, antioxidants, UV absorbers, radical scavengers and wetting agents. Essentially, the substances already listed for the powder clearcoat come into consideration here. In addition, auxiliaries, defoamers, dispersion aids, biocides, solvents and neutralizing agents can be added to the aqueous phase. Modified polysiloxanes are preferred as defoaming agents. Dispersion aids are e.g. preferably ammonium or metal salts of polycarboxylates. Neutralizers that can be used are amines, ammonia and metal hydroxides.

It is advantageous if the powder clearcoat slurry obtained has the following properties. The powder clearcoat has a glass transition temperature of 20 to 90 ° C, preferably 40 to 70 ° C. The powder clearcoat slurry has a viscosity of 10 to 1000 mPas, preferably 50 to 300 mPas at a shear rate of 500 s ^"1 and a solids content from 10 to 50%, preferably 20 to 40%. The powder clearcoat slurry obtained from the redispersion is optionally ground, while maintaining a temperature of 0 to 60 ° C., preferably 5 to 35 ° C., to a pH of 4.0 to 7.0, preferably 5.5 to 6.5 adjusted and filtered. The specific energy input during the grinding process is preferably from 20 to 500 Wh / kg. The average grain size obtained is between 1 and 25 μm, preferably less than 20 μm. Particularly preferred at 3 to 10 μm.

It is essential to the invention that the powder clearcoat slurry contains only small amounts of organic solvents, preferably less than 10% by weight, most preferably less than 5% by weight, ideally less than 1% by weight, based on that used in stage (B) Total amount of organic solvents.

0 to 5% by weight of a defoamer mixture, an ammonium and / or alkali salt, a carboxyl-functional or nonionic dispersing aid, wetting agent and / or thickener mixture and the other additives can be added to the dispersion before or after any wet grinding or the introduction into the dispersion medium be added. According to the invention, defoamers, dispersants, wetting agents and / or thickeners are preferably first dispersed in the dispersion medium. Then small portions of the powder clear coat are introduced. Then defoamers, dispersing aids, thickeners and wetting agents are added again. Finally, clear powder coatings are introduced again in small portions. The pH is preferably adjusted with ammonia or amines. The pH value can initially rise here, resulting in a strongly basic dispersion. However, the pH falls back to the above values within several hours or days.

The powder clearcoat dispersions described in water are particularly suitable as a dispersion medium for waterborne basecoats based on a polyester, polyurethane resin and an aminoplast resin.

The powder clearcoat slurries applied to a basecoat are regularly flashed off before baking. This is expediently done first at room temperature and then at a slightly elevated temperature. As a rule, the elevated temperature is 40 to 70 ° C., preferably 50 to 65 ° C. The flash off is carried out for 2 to 10 minutes, preferably 4 to 8 minutes at room temperature. At an elevated temperature, the mixture is vented again during the same time period. The baking can be carried out at temperatures below 130 ° C. The stoving can also be carried out at 130 to 180 ° C., preferably 135 to 155 ° C. Layer thicknesses of 30 to 50, preferably 35 to 45 μm can be achieved.

On the other hand, practically all clearcoats which are available in solution or dispersion in an organic solvent can be used as clearcoats. The usual one-component or multi-component clearcoats come into question. With regard to suitable one-component clearcoats, reference is made, for example, to the literature reference DE 195 29 124 Cl. In general, however, there are also clear coats made from hydroxy-functional ones Polyacrylates and blocked and / or unblocked polyisocyanates, for example free isocyanate trimers of hexamethylene diisocyanate, or customary clear lacquers which are crosslinked by aminoplast resin, for example crosslinked by melamine resin, can be used.

In particular, clear coats of the following basic structure are preferred. In this respect, preferred clear coats are a component system which is characterized in that a first component (I) is formed from the hydroxy-functional binder or the mixture of hydroxy-functional binders (1), and that a second component (II) is formed from the free (poly) isocyanates or the mixture of free (poly) isocyanates (3) is formed, and that a third component (III) is formed from the tris (alkoxycarbonylamino) triazine or the mixture of tris (alkoxycarbonylamino) triazines (2). If all components I to III are initially separate, then it is a 3-component system. However, component III can also be added to component I and / or component II from the outset. Then it is a two-component system. If, on the other hand, all components I to III are mixed from the outset, it is a one-component system. In the case of a multi-component system, the components can either be immediately before the solution or Dispersion can be mixed in critical or supercritical carbon dioxide or the components can first be dissolved or dispersed separately in critical or supercritical carbon dioxide. In the latter case, the components are mixed or stage (D) ff. Is carried out shortly before application. in case of a 1-component system, the components can be brought together in one of the stages (A) to (D).

For the hydroxy-functional binder or for the mixture of hydroxy-functional binders, preference is given to those from the group "binders based on hydroxy-functional polyacrylates, hydroxy-functional polyesters and / or hydroxy-functional polyurethanes" and / or mixtures of elements from this group and / or mixtures of different binders of one element thereof Group considered.

Polyacrylate resins are preferably used, the hydroxyl numbers from 40 to 240, preferably 60 to 210, very particularly preferably 100 to 200, acid numbers from 0 to 35, preferably 0 to 23, very particularly preferably 3.9 to 15.5, glass transition temperatures of -35 to +70 ° C, preferably -20 to +40 ° C, very particularly preferably -10 to +15 ° C and number average molecular weights of 1500 to 30,000, preferably 2000 to 15000, very particularly preferably 2500 to 5000.

The glass transition temperature of the polyacrylate resins is determined by the type and amount of the monomers used. The selection of the monomers can be approximated by a person skilled in the art in the usual way. Measures to control the molecular weight (eg selection of appropriate polymerization initiators, use of chain transfer agents, etc.) are part of the specialist knowledge of the person skilled in the art and need not be explained in more detail here. The hydroxy-functional binder component used is, for example, polyester resins or alkyd resins which can be prepared by (al) a cycloaliphatic or aliphatic polycarboxylic acid or a mixture of such polycarboxylic acids (b1) an aliphatic or cycloaliphatic polyol with more than two hydroxyl groups in the molecule or a mixture from such polyols (cl) an aliphatic or cycloaliphatic diol or a mixture of such diols and (dl) an aliphatic linear or branched saturated monocarboxylic acid or a mixture of such monocarboxylic acids in a molar ratio of (al): (bl): (cl) : (dl) = 1.0: 0.2 - 1.3: 0.0 - 1.1: 0.0 - 1.4, preferably 1.0: 0.5 - 1.2: 0.0 - 0.6: 0.2-0.9 to be converted into a polyester resin or alkyd resin. Examples of component (al) are: hexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid, endomethylene tetrahydrophthalic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. Examples of component (bl) are:

Pentaerythritol, trimethylolpropane, trimethylolethane and Glyceπn. Examples of constituent (cl) are: ethylene glycol, diethylene glycol, propylene glycol, neopentyl glycol, 2-methyl-2-propylpropanediol-1, 3, 2-ethyl-2-butylpropanediol-1, 3, 2, 2, 4-tπmethyl - Pentanediol-1, 5, 2.2, 5-trimethylhexanediol-1, 6, hydroxypivalic acid neopentylglycol ester and dimethylolcyclohexane. Examples of component (dl) are: 2-ethylhexanoic acid, lauric acid, isooctanoic acid, isononanoic acid and monocarboxylic acid mixtures which are obtained from coconut oil or palm kernel oil. The production of hydroxyl group-bearing polyester and / or alkyd resins is described, for example, in Ulimann's Encyclopedia of Industrial Chemistry, third edition, 14th volume, Urban & Schwarzenberg, Munich, Berlin 1963, pages 80 to 89 and pages 99 to 105, in the books: Resines

Alkydes-Polyesters by J. Bourry, Paris Verlag Dunod 1952, Alkyd Resins by C.R. Martens, Reinhold Publishing Corporation, New York 1961 and Alkyd Resin Technology by T.C. Patton, Interscience Publishers 1962.

The hydroxy-functional binder component used is, for example, polyacrylate resins which can be prepared by (a2) 10 to 92, preferably 20 to 60% by weight of an alkyl or cycloalkyl acrylate or an alkyl or cycloalkyl methacrylate having 1 to 18, preferably 4 to 13 carbon atoms in the Alkyl or cycloalkyl radical or mixtures of such monomers, (b2) 8 to 60, preferably 12.5 to 38.5% by weight of a hydroxyalkyl acrylate or a hydroxylalkyl methacrylate having 2 to 4 carbon atoms in the hydroxyalkyl radical or mixtures of such Monomers, (c2) 0.0 to 5.0, preferably 0.7 to 3.0% by weight of acrylic acid or methacrylic acid or mixtures of these monomers and (d2) 0 to 50, preferably 0 to 30% by weight of (a2), (b2) and (c2) various ethylenically unsaturated monomers copolymerizable with (a2), (b2) and (c2) or mixtures of such monomers to give polyacrylate resins having hydroxyl numbers of 40 to 240, preferably 60 to 150, Acidity select from 0 to 35, preferably from 5 to 20, glass transition temperatures from -35 to +70 degrees C, preferably from -20 to +40 degrees C and number average molecular weights from 1500 to 30,000, preferably from 2000 up to 15000, (determined by gel permeation chromatography using a polystyrene standard). Examples of (a2) components are: methyl, ethyl, propyl, n-butyl, isobutyl, tert. -Butyl-, pentyl-, hexyl-, heptyl- and 2-ethyl-hexyl acrylate or methacrylate as well as cyclohexyl acrylate and cyclohexyl methacrylate. Examples of (b2) components are: hydroxyethyl, hydroxypropyl and hydroxybutyl acrylate or methacrylate. Examples of (d2) components are: vinylaromatics, such as, for example, styrene, vinyltoluene, alpha-methylstyrene, alpha-ethylstyrene, nucleus-substituted diethylstyrenes, isopropylstyrene, butylstyrenes and methoxystyrenes; Vinyl ethers such as, for example, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether and

Isobutyl vinyl ether and vinyl esters, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate and the vinyl ester of 2-methyl-2-ethylheptanoic acid. The person skilled in the art can easily control the hydroxyl number and the acid number of the polyacrylate resins by the amount of component (b2) or (c2) used.

Polyhydroxy resins which can be obtained by (AI) 10 to 51% by weight, preferably 25 to 41% by weight, 4-hydroxy-n-butyl acrylate or 4-hydroxy-n-butyl methacrylate or a mixture of 4-hydroxy-n-butyl acrylate and 4-hydroxy-n-butyl methacrylate, preferably 4-hydroxy-n-butyl acrylate, (A2) 0 to 36% by weight, preferably 0.1 to 20% by weight, one of (AI) different hydroxyl-containing esters of acrylic acid or one hydroxyl-containing ester of methacrylic acid or one Mixture of such monomers, (A3) 28 to 85% by weight, preferably 40 to 70% by weight, of an aliphatic or cycloaliphatic ester of methacrylic acid which is different from (AI) and (A2) and has at least 4 carbon atoms in the alcohol radical or one Mixture of such monomers, (A4) 0 to 3% by weight, preferably 0.1 to 2% by weight, of an ethylenically unsaturated carboxylic acid or a mixture of ethylenically unsaturated carboxylic acids and (A5) 0 to 20% by weight, preferably 5 to 15% by weight of an unsaturated monomer different from (AI), (A2), (A3) and (A4) or a mixture of such monomers to form a polyacrylate resin having a hydroxyl number of 60 to 200, preferably 100 to 160 , an acid number from 0 to 35, preferably from 0 to 25, and a number average molecular weight from 1500 to 10,000, preferably 2500 to 5000, are polymerized, the sum of the parts by weight of components (AI) to (A5) always giving 100% and the composition of the component (A3 ) is selected so that when component (A3) is polymerized alone, a polymethacrylate resin with a glass transition temperature of +10 to +100 degrees C, preferably of +20 to +60 degrees C, is obtained. Examples of component (A2) are: hydroxyalkyl esters of acrylic acid, such as, for example, hydroxyethyl acrylate and hydroxypropyl acrylate, and hydroxyalkyl esters of methacrylic acid, such as, for example, hydroxyethyl methacrylate and hydroxypropyl methacrylate, the choice to be made such that when component (A2) is polymerized alone, a polyacrylate resin with a glass transition temperature of 0 to +80 degrees C, preferably from +20 to +60 degrees C. Examples of component (A3) are: aliphatic esters of methacrylic acid with 4 to 20 carbon atoms in the alcohol residue, such as n-butyl, iso-butyl, tert. -Butyl, 2-ethylhexyl, stearyl and lauryl methacrylate, and cycloaliphatic esters of methacrylic acid such as, for example, cyclohexyl methacrylate. Acrylic acid and / or methacrylic acid are preferably used as component (A4). The following are examples of component (A5): vinylaromatic hydrocarbons, for example styrene, α-alkylstyrene and vinyltuluol, amides of acrylic acid and methacrylic acid, for example methacrylamide and acrylamide, nitriles of acrylic acid and methacrylic acid, vinyl ethers and vinyl esters. Vinylaromatic hydrocarbons, in particular styrene, are preferably used as component (A5). The composition of component (A5) should preferably be such that when alone

Polymerization of component (A5) a polymer with a glass transition temperature of +70 to +120 degrees C, preferably from +80 to +100 degrees C is obtained. These polyacrylate resins can be prepared by generally known polymerization processes (see, for example, Houben-Weyl, Methods of Organic Chemistry, 4th Edition, Volume 14/1, pages 24 to 255 (1961)). They are preferably produced using solvent polymerization. An organic solvent or solvent mixture is usually initially introduced and heated to boiling. The monomer mixture to be polymerized and one or more polymerization initiators are then continuously added to this organic solvent or solvent mixture. The polymerization is carried out at temperatures between 100 and 160 degrees C, preferably between 130 and 150 degrees C. As initiators, free radical initiators are preferably used. The type and amount of initiators are usually chosen so that the supply of radicals is as constant as possible at the polymerization temperature during the feed phase. Examples of initiators which can be used are: dialkyl peroxides, for example di-tert. -Butyl peroxide and dicumyl peroxide, hydroperoxides, for example cumene hydroperoxide and tert. -Butyl hydroperoxide, perester, eg tert. Butyl perbenzoate, tert. Butyl perpivalate, tert. -Butylper-3, 5, 5-trimethylhexanoate and tert. -Butylper-2-ethylhexanoate. The polymerization conditions (reaction temperature, feed time of the monomer mixture, amount and type of organic solvents and polymerization initiators, possibly also the use of molecular weight regulators, for example mercaptans, thioglycolic acid esters and hydrogen chloride) are selected so that the polyacrylate resins have a number average molecular weight as indicated (determined by gel permeation chromatography using Have polystyrene as calibration substance). The acid number can be adjusted by the person skilled in the art by using appropriate amounts of component (A4). The same applies to the setting of the hydroxyl number. It can be controlled via the amount of component (AI) and (A2) used.

Binders based on polyurethane are also suitable.

Finally, it is important for the clear lacquer which is preferred in this respect that the coating composition contains components (2) and (3), both of which are crosslinking agents.

Tris (alkoxycarbonylamino) triazines of the formula are used as component (2)

used, R being in particular methyl and butyl groups. These compounds are known under the short name TACT. Derivatives of the named

Connections are used. Tris (alkoxycarbonyla ino) triazines such as are described in US Pat. No. 5,084,541 are preferably used for the component (2).

Component (3) contains at least one non-blocked di- and / or polyisocyanate as crosslinking agent, optionally dissolved or dispersed in one or more organic, optionally water-dilutable solvents. In addition or in its place, blocked isocyanate or a mixture of blocked polyisocyanates can also be used.

The free polyisocyanate component used is any organic polyisocyanate with aliphatic, cycloaliphatic, araliphatic and / or aromatically bound free isocyanate groups. Polyisocyanates with 2 to 5 isocyanate groups per molecule and with viscosities of 100 to 2000 Pa.s (at 23 degrees C) are preferably used. If necessary, small amounts of organic solvent, preferably 1 to 25% by weight, based on pure polyisocyanate, can also be added to the polyisocyanates, in order to ensure that the isocyanate can be incorporated to improve and, if necessary, lower the viscosity of the polyisocyanate to a value within the above-mentioned ranges. Solvents suitable as additives for the polyisocyanates are, for example, ethoxyethyl propionate, butyl acetate and the like. Examples of suitable isocyanates are, for example, in "Methods of Organic Chemistry", Houben-Weyl, Volume 14/2, 4th Edition, Georg Thieme Verlag, Stuttgart 1963, pages 61 to 70, and by W. Siefken, Liebigs Ann. Chem. 562, 75 to 136. For example, those at

Description of the polyurethane resins (A2) called isocyanates and / or polyurethane prepolymers containing isocyanate groups, which can be prepared by reacting polyols with an excess of polyisocyanates and which are preferably low-viscosity. It can too

Polyisocyanates containing isocyanurate groups and / or biuret groups and / or allophanate groups and / or urethane groups and / or urea groups and / or uretdione groups can be used. Polyisocyanates containing urethane groups are obtained, for example, by reacting some of the isocyanate groups with polyols, such as trimethylolpropane and glycerol. Aliphatic or cycloaliphatic polyisocyanates, in particular hexamethylene diisocyanate, dimerized and trimerized hexamethylene diisocyanate, isophorone diisocyanate, 2-isocyanatopropylcyclohexyl isocyanate, dicyclohexyl methane-2, 4'-diisocyanate or dicyclohexyl methane-4-isocyanate or mixtures of these, 4 ', or 4'-mixtures of these, are used. Mixtures of uretdione and / or isocyanurate groups and / or allophanate groups containing polyisocyanates based on hexamethylene diisocyanate, such as those obtained by catalytic Oligomerization of hexamethylene diisocyanate using suitable catalysts are used. The polyisocyanate component can also consist of any mixtures of the free polyisocyanates mentioned by way of example.

If blocked isocyanate is admixed, it is preferably designed such that it contains isocyanate groups blocked with both a blocking agent (ZI) and with a blocking agent (Z2), the blocking agent (ZI) being a dialkylmalonate or a mixture of dialkylmalonates the blocking agent (Z2) is a blocking agent containing active methylene groups other than (ZI), an oxime or a mixture of these blocking agents and the equivalent ratio between the isocyanate groups blocked with (ZI) and the isocyanate groups blocked with (Z2) is between 1.0 : 1.0 and 9.0: 1.0, preferably between 8.0: 2.0 and 6.0: 4.0, particularly preferably between 7.5: 2.5 and 6.5: 3.5 . The blocked isocyanate is preferably made as follows. A polyisocyanate or a mixture of polyisocyanates is reacted in a manner known per se with a mixture of the blocking agents (ZI) and (Z2), the mixture of the blocking agents (ZI) and (Z2) being the blocking agents (ZI) and ( Z2) in a molar ratio which is between 1.0: 1.0 and 9.0: 1.0, preferably between 8.0: 2.0 and 6.0: 4.0, particularly preferably between 7, 5: 2.5 and 6.5: 3.5. The polyisocyanate or the mixture of polyisocyanates can be mixed with the mixture of

Blocking agents (ZI) and (Z2) are reacted until no more isocyanate groups can be detected. In the In practice, this can require the use of very large excesses of blocking agents and / or very long reaction times. It was found that paints with good properties are obtained even if at least 50, preferably at least 70 percent of the isocyanate groups of the polyisocyanate or the mixture of polyisocyanates are reacted with the mixture of blocking agents (ZI) and (Z2) and the remaining isocyanate groups be reacted with a compound containing hydroxyl groups or a mixture of compounds containing hydroxyl groups. Low-molecular-weight aliphatic or cycloaliphatic polyols, such as neopentyl glycol, dimethylolcyclohexane, ethylene glycol, diethylene glycol, propylene glycol, 2-methyl-2-propyl-propanediol-1, 3, 2-ethyl-2-butyl-propanediol-1, 3, 2, 2, 2, are preferably used as compounds containing hydroxyl groups. 2, 4-trimethylpentanediol-1, 5 and 2, 2, 5-trimethylhexanediol-1, 6 or the binder containing hydroxyl groups which can be used as component (1). A suitable blocked polyisocyanate is also obtainable by mixing blocked polyisocyanates with the blocking agent (ZI) or (Z2) in such a ratio that a mixture is obtained in which the equivalent ratio between the isocyanate groups blocked with (ZI) and the isocyanate groups blocked with (Z2) between 1.0: 1.0 and 9.0: 1.0, preferably between 8.0: 2.0 and 6.0: 4.0, particularly preferably between 7.5: 2 , 5 and 6.5: 3.5. In principle, all polyisocyanates that can be used in the coating field can be used to produce the blocked polyisocyanate. However, it is preferred to use polyisocyanates whose isocyanate groups are bonded to aliphatic or cycloaliphatic radicals. Examples of such polyisocyanates are hexamethylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexyl methane diisocyanate and 1,3-bis (2-isocyanatopropyl-2-) benzene (TMXDI) and adducts of these polyisocyanates with polyols, especially low molecular weight polyols, such as trimethylol propane these polyisocyanates derived isocyanurate group and / or biuret group-containing polyisocyanates. Particularly preferred polyisocyanates are hexamethylene diisocyanate and isophorone diisocyanate, isocyanurate or biuret group-containing polyisocyanates derived from these diisocyanates, which preferably contain more than two isocyanate groups in the molecule, and reaction products of hexamethylene diisocyanate and isophorone diisocyanate or a mixture thereof

Hexamethylene diisocyanate and isophorone diisocyanate with 0.3-0.5 equivalents of a low molecular weight polyol with a molecular weight from 62 to 500, preferably from 104 to 204, in particular a triol, such as trimethylolpropane, are used. Dialkyl malonates or a mixture of dialkyl malonates are used as blocking agents (ZI). Dialkylmalonates with 1 to 6 carbon atoms in each of the alkyl radicals are mentioned as examples of dialkylmalonates which can be used, e.g. Malonic acid dimethyl ester and malonic acid diethyl starch, with malonic acid diethyl ester being preferred. The blocking agents (Z2) used are blocking agents and oximes which contain active methylene groups and mixtures of these blocking agents and which are different from (ZI). As examples of blocking agents used as

Blocking agents (Z2) that can be used are mentioned: methyl, ethyl, propyl, butyl, pentyl, acetoacetic acid, hexyl, heptyl, octyl, nonyl, decyl or dodecyl ester, acetone oxime, methyl ethyl ketoxime, acetylacetone, formal doxime, acetaldoxime, benzophenoxime, acetoxime and diisobutyl ketoxime. The blocking agent (Z2) used is preferably an alkyl acetoacetate having 1 to 6 carbon atoms in the alkyl radical or a mixture of such alkyl acetoacetates or a ketoxime or a mixture of ketoximes. Ethyl acetoacetate or methyl ethyl ketoxime are particularly preferably used as blocking agents (Z2).

It is preferred if the amounts of constituents (1) to (3) in the ratios to one another are chosen such that the ratio OH: (NCO + NH-CO-OR) 1.0: 0.5 to 1.0: 2.0, preferably 1.0: 0.8 to 1.0: 1.5. The

Polyisocyanate component is used in the coating compositions according to the invention e.g. individually advantageously used in such an amount that the ratio of the hydroxyl groups of the binder (1) to the isocyanate groups of the crosslinking agents (2) and (3) is between 1: 2 and 2: 1, particularly preferably between 1: 1.5 and 1 , 5: 1 lies.

The quantitative ratio of the components (2) and (3) to one another is advantageously selected such that the amount of tris (alkoxycarbonylamino) triazine or of a mixture of tris (alkoxycarbonylamino) triazines is 1 to 99% by weight, preferably 5 to 90% by weight, is, based on the total amount of tris (alkoxycarbonylamino) triazine or mixture of tris (alkoxycarbonylamino) triazines plus free isocyanates or the mixture of free polyisocyanates. If blocked isocyanates are added or if they are used alone, the same applies, only then related to the corresponding total amount of isocyanates instead of just free polyisocyanates.

The quantitative ratios mentioned above relate to the quantitative ratios which are obtained when the components (I) to (III) are mixed in the paint that can be applied or applied. Multi-component systems are namely regularly sold in containers, each of which, in total or in part, mixed with the lacquer with the desired proportions of the components, so that no part of one of the components remains when the other component or components are used up. In other words, the proportions (1) to (3) in components I to III of a multi-component container are defined by the above quantitative ratios.

In detail, the component system can contain UV absorbers, preferably triazine compounds, and free radical scavengers in at least one of components (I) and / or (II) and / or (III). The component system can also contain rheological agents and other paint auxiliaries in at least one of components (I) and / or (II) and / or (III).

Coatings obtained with the clear coats described above are usually cured at temperatures below 120 ° C., preferably at temperatures not exceeding 100 ° C. In application forms of the invention

Coating agents with blocked polyisocyanates and / or with TACT can also be used at higher curing temperatures become. Then values from 120 degrees C to 180 degrees C are recommended.

Exemplary embodiments of clear lacquer binders or clear lacquers which are suitable in the context of the invention are given below.

1. Clear varnish binder dissolved or dispersed in an organic solvent

1.1 Component I

1.1.1. Acrylate resin A In a laboratory reactor with a useful volume of 4 1 equipped with a stirrer, two dropping funnels for the monomer mixture or. Initiator solution, nitrogen inlet tube, thermometer and reflux condenser are weighed in 899 g of a fraction of aromatic hydrocarbons with a boiling range of 158 ° C - 172 ° C. The solvent is heated to 140 ° C. After reaching 140 ° C., a monomer mixture of 727 g of n-butyl methacrylate, 148 g of cyclohexyl methacrylate, 148 g of styrene, 445 g of 4-hydroxibutyl acrylate and 15 g of acrylic acid are added within 4 hours, and an initiator solution of 29 g of t Butyl perethylhexanoate in 89 g of the aromatic solvent described is metered uniformly into the reactor within 4.5 hours. The metering of the monomer mixture and the initiator solution is started simultaneously. After the initiator metering has ended, the reaction mixture is held at 140 ° C. for a further two hours and then cooled. The resulting polymer solution has a solids content of 62% (determined in a convection oven for 1 h at 130 degrees C), an acid number of 9 and a viscosity of 21 dPa.s (measured on a 60% solution of the polymer solution in the aromatic solvent described, using an ICI plate cone viscometer at 23 degrees C).

1.1.2. Acrylate resin B

In a laboratory reactor with a useful volume of 4 1 equipped with a stirrer, two dropping funnels for the monomer mixture or. Initiator solution, nitrogen inlet tube, thermometer and reflux condenser are weighed in 897 g of a fraction of aromatic hydrocarbons with a boiling range of 158 ° C - 172 ° C. The solvent is heated to 140 degrees C, after reaching 140 degrees C, a monomer mixture of 487 g t-butyl acrylate, 215 g n-butyl methacrylate, 143 g styrene, 572 g hydroxypropyl methacrylate and 14 g acrylic acid within 4 hours, and an initiator solution of 86 g of t-butyl perethyl hexanoate m 86 g of the aromatic solvent described evenly metered into the reactor within 4.5 hours. The metering of the monomer mixture and the initiator solution are started simultaneously. After the initiator metering has ended, the reaction mixture is kept at 140 ° C. for a further two hours and then cooled. The resulting polymer solution has a solids content of 62%, determined in a forced air oven for 1 h at 130 ° C., an acid number of 10 and a viscosity of 23 dPa.s (measured on a 60% solution of the polymer solution in the aromatic solvent described , using an ICI Piatte cone viscometer at 23 degrees C). 1.1.3. Alkyd resin C

In a laboratory reactor with a useful volume of 4 1 equipped with a stirrer, water separator, reflux condenser, nitrogen inlet tube and thermometer, 1330 g of hexahydrophthalic anhydride, 752 g of 1, 1, 1-trimethylolpropane, 249 g of 1, 4-dimethylolcyclohexane, 204 g Hexanediol-1, 6, 136 g of isononanoic acid (as an isomer mixture of 3, 3, 5-trimethylhexanoic acid and 3, 5, 5-trimethylhexanoic acid) and 75 g of xylene as entrainer weighed out. The water separator is filled with xylene. The contents of the reactor are heated to 210 degrees C in the course of 8 hours in such a way that a uniform reflux of the entrainer occurs. The reactor contents are kept at 210 ° C. until an acid number of 17.1 and a viscosity of 15 dPas, measured on a 60% solution of the reaction mixture in the aromatic solvent described in the acrylic resins A and B, is reached. The mixture is then cooled to 140 ° C. and the contents of the reactor are dissolved with so much of the aromatic solvent mentioned that a non-volatile fraction of 61% (determined in a convection oven for 60 minutes at 130 ° C.) results. The alkyd resin solution prepared in this way has one Acid number of 17.1 and a viscosity of 15 dPa.s (measured on an ICI-plate-cone viscometer at 23 degrees C).

1.1.4 Component I

Component (I) is produced by using the basic binder solution according to 1.1.1 and / or 1.1.2 and / or 1.1.3. weighed in, then with stirring add solvent, UV absorber, radical scavenger and leveling agent in the usual amounts and stir well. 1.2. Component (II)

Component (II) consists of a solution of commercially available isocyanurate trimers in a suitable solvent. It is produced by stirring the solvent into the 5 delivery form of the isocyanurates.

1.3 component (III)

Component (III) consists of a (hand ice) usual solution of tris (alkoxycarbonylamino) triazine crosslinking agent according to US 10 5084541, optionally in a suitable solvent, such as

Solvent naphtha, butyl acetate, Basonat HI 190 B / S and / or Tolonate HDT 90.

15 2. Coating a substrate with a clear lacquer dissolved or dispersed in critical or supercritical carbon dioxide.

After their production, components I to III are separated in 20 organic solution or dissolved or dispersed together in critical or supercritical carbon dioxide by means of a jet nozzle reactor. Then the majority of the organic solvents are separated from the dispersion or dispersions. If necessary, another 25 critical or supercritical carbon dioxide is added. The dispersion or dispersions obtained in this way are then introduced into an aqueous phase, which may contain other suitable paint additives. The powder coating slurry obtained in this way is then applied to the substrate, a motor vehicle body part, which is coated with a primer, a filler and a color coating, by spraying. If with separate aqueous dispersions usual, adapted multi-component application devices can be used. After curing or baking, a clear lacquer coating that meets all requirements is obtained with the lowest emissions of organic solvents.